The present invention is related to optical networks and, in particular, to optical networks with multimode optical fibers.
Today most optical fibers being installed are single-mode optical fibers. This is especially true for the so-called long-haul networks, such as the optical networks which form the backbone of national and international communications networks. In contrast, much of the legacy optical fibers are multimode optical fibers. Over 80% of the optical fiber cabling installed for local area networks is multimode optical fiber.
The quality of links made from multimode fibers is problematical and difficult to predict. As a matter of fact, in single-mode fiber systems chromatic dispersion is the parameter which effectively and predictably characterizes the linear performance propagation of optical signals through a network link. As chromatic dispersion increases, the bit error rate (BER) increases. On the contrary, multimode fibers have no such parameter nor testing methodology to forecast the performance of a multimode fiber link.
Furthermore, the current increase in data transfer rates, i.e., past 1 Gbps (Gigabits per second) toward 10 Gbps and beyond, and the use of laser sources for such high-speed transmissions, as opposed to low-rate LED (Light-Emitting Diode) sources, have further exacerbated this problem for multimode fibers of which there are many different performance types. Many deployed multimode fibers are not readily suitable for 10 Gbps rates. Modal dispersion, the distortion of a signal propagating along the different modes of a multimode fiber, is accentuated by higher bit rates and multimode fibers are sensitive to how signals are launched into the fibers, i.e., what light sources are used for the generation of optical signals in the fibers.
Some way of ascertaining the quality of a multimode fiber link is very desirable to determine whether the link can carry the signals as required in a high-speed network. Furthermore, it should be practical and inexpensive for convenient in situ usage in real multimode fiber network systems, as compared to laboratory systems.
The present invention is directed toward a probe for multimode fibers so that the quality of multimode fiber links can be determined and high-speed systems, such as 10 Gbps systems, can operate effectively over multimode fibers. The probe is practical and inexpensive.